(In reply to comment #5)
> (From update of attachment 75427[details])
> View in context: https://bugs.webkit.org/attachment.cgi?id=75427&action=review
>
> I don’t want to see these renderer classes added until we are sure we need them. Are you certain you will need all three?
The plan is to RenderDetails to use RenderBlock::layoutSpecialExcludedChild() to set the position of its first RenderSummary child. And this first RenderSummary creates a RenderDetailsMarker in a way similar to what is done by RenderListItem.
What do you think?

Comment on attachment 75464[details]
patch
I’m still not sure I understand if this will require all three unique renderer classes. At the moment we are just checking them in as dead code which seems a little weak.
r=me, but please find out why the Windows build is failing and resolve that before checking in